1. Field of Invention
The invention relates to shifting means for achieving locked connection of at least two shafts whereby the shafts have different rotation speeds at the start of a shift procedure, and also to the use of such shifting means in power takeoff (PTO) and other drive systems for utility vehicles and, in particular, for agricultural tractors.
2. Description of Related Art
For many years agricultural tractors have been fitted with PTO systems which allow the transfer of torque from the prime mover to an attached implement. Examples of implements that utilise PTO systems include balers, fertilizer spreaders, seed drills and hedge cutters to name but a few.
Some implements, tillage implements for example, are power hungry and place a constant high load upon the PTO typically operating at the nominal engine speed to deliver the optimum efficiency. Other implements such as fertilizers spreaders place a low load upon the PTO but still demand the maximum speed. The demanded PTO speed dictates the speed at which the engine must be run due to the direct mechanical connection between the engine and the output PTO stub. In the case of low load at applications this results in excessive fuel consumption and noise.
Some implements demand a constant ratio between the groundspeed and the PTO speed. Some tractors provide a groundspeed PTO mode wherein the propulsion drive to the wheels is directly coupled by meshed gears to the PTO stub. The ratio between groundspeed and PTO speed in such a mode is fixed by the gears installed during manufacture and the size of tyre fitted.
Where a groundspeed PTO mode is provided, problems may occur when switching between groundspeed and engine speed.
It is an object of the invention to provide a mechanism for switching of coaxial shafts in applications such as a PTO drive system for a utility vehicle such as an agricultural tractor which at least alleviates some the aforementioned problems.